(1) Field of the Invention
The present invention relates to a method for runnerless injection molding of a synthetic resin by an intermittent cooling system and an apparatus thereof.
(2) Description of the Prior Art
Methods for runnerless injection molding of a synethic resin and the apparatus thereof include an apparatus called "Spear System" as the registered trade name, and a method using the apparatus developed by the inventor.
The conventional apparatus is provided with an intermittent heating mechanism, which is capable of local heating of a gate. In the runnerless injection molding apparatus the molten synthetic resin is continuously injection-molded by an injection mechanism, with the intermittent heating mechanism the resin which has cooled and solidified in the gate to shut the gate is intermittently heated for every molding operation to be molten, whereby the gate is opened for enabling the injection of the molten resin into cavities. With the apparatus, the heating operation of the intermittent heating mechanism is stopped immediately after the finish of the injection molding operation to permit cooling solidification of the resin in a minute amount in the gate, and the gate is shut for performing several operations such as mold-opening and removal of the molded product. This prevents the leakage of the molten resin whereby a highly precise product free of sprue runners can continuously be molded.
The above-described "Spear System" necessitates electric control by means of a heater because it performs both gate-opening and closing operations in the case of local melting and solidification of a minute amount of a resin by means of the intermittent heating means of an intermittent heating mechanism and the heater means may be of a small scale because it aims at a minute amount of the resin in the gate. In spite of the above advantage, several problems are encountered for reducing costs such as indispensability of expensive electric parts e.g. a transformer for electric control and a controller for intermittent heating.